A light- and heat-sensitive recording material which can be image-exposed and thereafter developed by uniformly heating to provide images is called photothermography (a light- and heat-sensitive image-forming process) and has the feature that images are obtained simply by dry processing.
JP-A No. 59-190886 discloses such a process using a recording material having light- and heat-sensitive layer comprising microcapsules containing diazo compounds and fine dispersion of couplers capable of forming dye by diazo reaction. In this process, for obtaining an image, the recording material is heated to transfer the dispersed coupler into the microcapsules after photolyzing diazo compounds by exposure, to react the coupler with diazo compounds. However, this process needs a large amount of light for photolyzing diazo compounds.
A light hardenable composition can be used for producing a recording material having higher light-sensitivity.
A process of forming visible images by heat development using a photopolymerizable composition and a heat-sensitive coloring material is known as disclosed in JP-A No. 52-89915 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). In the process, a material wherein the two components of a two-component type heat-sensitive coloring material (e.g., an electron acceptive compound and an electron donative colorless dye) are separately disposed within and outside of microcapsules containing a light hardenable composition is imagewise exposed and heated. As a result, the light-exposed portions are not colored since these portions are hardened and thus a heat-sensitive component does not move in the portions. However, the heat-sensitive component moves in the unexposed portions undergoing reaction and coloring, whereby images are formed.
However, in this process, even if the light hardenable composition inside the microcapsules is sufficiently hardened, it is difficult to sufficiently restrain coloring at the light hardened portions on heat development. Thus indistinct images with a large amount of background fog are obtained.
Also, another technique involves a recording material having thereon a layer comprising a photopolymerizable composition composed of a vinyl monomer having an acid group and a photopolymerization initiator, a peeling layer and a layer comprising an electron donative colorless dye as disclosed in JP-A No. 61-123838. The recording material is imagewise exposed and uniformly heated for reaction with the leuco dye with an unpolymerized monomer having an acid group diffused therefrom, whereby a positive visible image is formed.
Also, a negative image can be obtained using the similar process as described in JP-A No. 60-119552.
In this method, the recording material wherein a photopolymerizable composition comprising a monomer (or premonomer) capable of bleaching a dye and a photopolymerization initiator and a dye to be bleached by the monomer are isolatedly present is imagewise exposed and uniformly heated. As a result, the monomer diffusing in the unpolymerized portion bleaches the dye to obtain a negative visible image.
However, in each of above two processes, coloring densities or degree of bleaching a dye is liable to decrease, therefore, the contrast of the image obtained is still low.
As a result of various investigations, an image has been obtained by coloring the light-hardened portions using a process comprising simply image exposure/heat development steps.
Also, for obtaining either positive image or negative one, while such light- and heat-sensitive recording materials may be used as a transfer type recording material using two sheets, it is preferred that at least two light- and heat-sensitive layers, each having a different light-sensitive wavelength and coloring hue, are present in a mono-sheet type multicolor recording material not requiring an extra sheet.
However, in the case of the mono-sheet type multicolor recording material, it is not easy to separate the light-sensitive wavelength regions of the light- and heat-sensitive layers from each other. That is, when known photopolymerization initiators or a known photopolymerization initiator/spectral sensitizer combination are used for the light- and heat-sensitive layers in the conventional manner, the light-sensitive wavelength regions of these layers overlap. As a result, it is difficult to photopolymerize each layer independently.
In this respect, addition of an ultraviolet absorbent to a light-sensitive composition is disclosed in U.S. Pat. No. 4,576,891. However, this point may be improved to some extent by this method but the overlap of the light-sensitive wavelength regions of the light- and heat-sensitive layers is still large.
This is because the unnecessary skirt at the short wavelength side of the light-sensitive region of each light-sensitive layer can be effectively cut but the skirt at the long wavelength side of each light-sensitive layer overlaps the light-sensitive wavelength regions of the layers.